Plasma processes for the preparation of diamond are well known and generally involve the use of a plasma to generate large amounts of necessary nonequilibrium gas-phase species such as atomic hydrogen. For example, plasma enhanced chemical vapor deposition has generally used a feedstock of a hydrocarbon-hydrogen mixture in forming the plasma to deposit diamond upon a target substrate. Recently researchers have used an essentially pure hydrogen plasma to convert a solid carbon form such as graphite or carbon black into diamond.
Together with the great interest in preparing diamond or coating substrates with diamond, there is also considerable interest in preparing diamond fibers or diamond-coated fibers, for example, diamond-coated graphite fibers. For example, Ting et al. in Diamond and Related Materials, 2 (1993), 1069-1077, describe diamond-infiltrated carbon-carbon composites including diamond coating of the carbon fibers within the carbon-carbon composite. Further, U.S. Pat. No. 4,957,591 describes a process for preparing needle-like or fibrous diamond by depositing columnar diamond and etching off the support or template.
It is an object of the present invention to provide a process of converting a solid hydrocarbon material to a diamond material or to a composite material including a diamond layer and a hydrocarbon layer.
It is a further object of the present invention to provide a process of converting a hydrocarbon fiber to a diamond fiber or a composite fiber including a diamond layer and a hydrocarbon layer.
It is a still further object of the invention to provide a graphite-free diamond fiber, a polycrystalline graphite-free diamond fiber, and fibers characterized in length from pulp, i.e., from about 1 mm to 5 mm, to staple, i.e., from about 0.25 inches to 1 inch, to continuous, i.e., of a length capable of being wound on, e.g., a bobbin.
Still a further object of the present invention is a layered structure including a layer of diamond and a layer of hydrocarbon material.